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Abstract

We present the first complete temporal and spatial characterization of the amplified spontaneous emission (ASE) of laser radiation generated by a diode-pumped high-power laser system. The ASE of the different amplifiers was measured independently from the main pulse and was characterized within a time window of −10ms ≤ t ≤ 10ms and an accuracy of up to 15fs around the main pulse. Furthermore, the focusability and the energy of the ASE from each amplifier was measured after recompression. Using our analysis method, the laser components, which need to be optimized for a further improvement of the laser contrast, can be identified. This will be essential for laser-matter interaction experiments requiring a minimized ASE intensity or fluence.

Figures (3)

Schematic layout of the Polaris laser system. An oscillator and a first amplifier are followed by a grating stretcher, four ns-amplifiers and a grating compressor. The pulses are finally focused by a parabolic mirror onto the target.

Amplification characterization of the first regenerative amplifier A1: photo diode measurement of the circulating pulse referenced to the output energy (black line); energy calibrated photo diode measurement of the ASE while the seed was blocked at the entrance (red line); corresponding ideal amplification of the respective measurement with the averaged small signal gain (black and red circles).

Combined log-log plot of the ASE for times t ≤ t0 (a) and times t ≥ t0 (b) regarding the different Polaris amplifiers. The insets show the respective spatial distribution which was measured in the focal plane of the main pulse. The ASE measurements were carried out with a photo diode/oscilloscope combination while the main pulse was measured with a 3rd-order cross-correlator.

Tables (1)

Table 1 Summary of the measured parameters relative peak intensity I/I0, energy E, duration τ, spot area A and q-factor of the several Polaris amplifiers as well as the average intensity Ī and fluence F̄ calculated from the measurement. The ASE parameters were carried out with the seed blocked before the amplifier to be characterized while all subsequent amplifiers were operating with their usual parameters.

Metrics

Table 1

Summary of the measured parameters relative peak intensity I/I0, energy E, duration τ, spot area A and q-factor of the several Polaris amplifiers as well as the average intensity Ī and fluence F̄ calculated from the measurement. The ASE parameters were carried out with the seed blocked before the amplifier to be characterized while all subsequent amplifiers were operating with their usual parameters.